This disclosure is directed to thermal and gaseous treatment of a plurality of wafers in batches under extremely clean production conditions. The disclosed apparatus and process have been designed to reduce the amount of wafer contamination, principally by particles released from reactor surfaces, during oxidation/diffusion and low pressure chemical vapor deposition (LPCVD) processes.
An alternate vertical furnace design that preceded this invention is illustrated in U.S. Pat. No. 4,738,618, issued to Robert G. Massey et al. on Apr. 19, 1988. This patent discloses a vertically oriented thermal processor, including a vertically adjustable furnace assembly and process tube. The process tube, in the form of a quartz bell jar, can be moved vertically up and down in the supporting framework in conjunction with the furnace assembly. Both the furnace assembly and process tube can also be moved up and down independently of one another.
One problem that has been identified with respect to certain applications of the thermal processor shown in U.S. Pat. No. 4,738,618 is the deposition of contaminants on the inner surface of the quartz process tube during certain treatment procedures. Such deposition in itself is not detrimental to the process, but the subsequent flaking off of the deposited materials during cooling and heating of the process tube surfaces releases particle contaminants to a degree that is unacceptable in some treatment systems.
The present invention arose from a need to physically separate the areas in which wafers are pre-heated and post-cooled from the areas in which gaseous or vapor treatments are conducted. Such treatments can then be efficiently carried out within a clean process chamber not subjected to heating and cooling across temperature ranges at which deposited materials can be released from the surrounding inert surfaces.
A further advantage of the disclosed equipment is the ability to transfer wafers between sealed chambers under vacuum conditions that confirm the integrity of the seals to prevent wafer contamination.
In addition, the vertical nature of the thermal processor reduces heat and energy losses by maintaining the process chamber at an elevated position relative to the load locks within which the wafers are heated and cooled.